Superheterodyne radio signaling system



Feb. 19,; 1929. 1,703,078

a. L. BEERS SUPERHBTERODYNE RADIO SIGNALING SXSTEM Filed F9910, 1925 TNESSE INVENTOR I cfiorje L Bee/:3 W d w v BY I AT'ToRNEY Patented Feb. 19, 1929.

- UNITED STATES 1,703,078 PATENT OFFICE.

GEORGE L. BEERS, OF WILKINSBU'RG, PENNSYLVANIA, ASSIGNOR T WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CQRPORA'IION OF PENNSYLVANIA.

SUPERHETERODYNE RADIO SIGNALING SYSTEM.

Application filed February My invention relates to radio receiving systerns and particularly to superheterodyne receiving systems.

An object of my invention is to construct a radio receiving system in which provision is made for the prevention of the re-radiation of local oscillations.

Another object of my invention is to provide means for increasing the selectivity of a sensitive radio receiving system.

Another object of my invention is to 1mprove the ratio of signal strength to extraneous noises in a superheterodyne radio re ceiving system.

Another object of my invention is to provide means for the prevention of the radiation of the frequencies present in asuperheterodyne radio receiving apparatus.

Another object of my invention is to provide means for preventing the response of a superheterodyne radio receiving apparatus to undesired signals having frequencies which are heterodyned by harmonics of the oscillation generator frequency.

In the operation of the su erheterodyne radio receiving system, it has een found to be exceedingly sensitive and within certain limitations exceedingly selective. It has likewise been found to give a signal strength wlnch, in its ratio to extraneous noises, has

been equal to or better than previous apparatus but, as is the case with all radio appa-' ratus, a certain amount of noise has been found to be present.

Also the presence of a local oscillation generator, as a part of the receiving apparatus, has resulted in the radiation of radio frequency energy from the antenna system ofthe receiver, at the local oscillation frequency. This radiated energy, or the socalled re-radiated energy, is troublesome to near-by receivers producing objectionable noises, howls and W istles in them.

While the superheterodyne. radio receiving system has been found to be among the most selective known, it has not been found pos sible to construct the system in such way as to avoid absolutely all interfering signals. It has been found that a powerful near-by sending station will force oscillations in the antenna system which may be carried through the amplifier system to the phones or loud-speakers. It has also been found that even with the utmost care in construction, an oscillation generator produces more than 10, 1925. Serial No. 8,209.

one frequency. Itproduces the fundamental frequency to which it is tuned and also one or more harmonics of that frequency. When frequency for which the system is designed,

thereby causing troublesome interference.

My invention provides a construction which, by the addition of one element, simultaneously increases the selectivity of the system, prevents the re-radiation of the local oscillations and improves the ratio between the'strength of received signals and noises from static strays and tube noises.

Other objects and structural details will be apparent from the following description when read in connection With the accompanying drawing, wherein:

Figure 1 is a diagrammatic view of circuits and apparatus embodying a preferred form of my invention; and

Fig. 2 is a diagrammatic view of circuits and apparatus of a modification.

Referring to the drawings, a radio receptor 1, which may preferably be a loop antenna, is connected to an amplifier triode 2. A tuning condenser 3 is connected to the receptor -1 at the points of connection between it and the amplifier tube. A local oscillation generator 4 having an adjustable tuned oscillating circuit 5 is provided. The anode of the triode 2 is connected to an output coil 6 which is inductively associated with the input coil 7 of a heterodyne resolving detector 8. The inductor of the oscillatory circuit 5 is inductively associated with the coil 7. The resolving detector 8 has a coil 9 in its output circuit which is inductively associated with the input coil of an amplifier systeinll which, in'turn, is connected to a detector 12 and signal translator 14. The coil 7 is shunted by a tuning condenser 15.

The condensers 3 and 15 are suitably chosen with respect to the antenna 1 and the coil 7 and are such that equal movements of the mechanical portions thereof produce equal changes in the resonant frequencies of the circuits of which they are parts. They are then mechanically connected to a single control and indicating means, whereby the resonant frequencies of the two circuits are kept substantially equal over the tuning range. I

In the embodiment shown in Fig. 1 an additional coil 16 is connected to the terminal of coil 6 and inductively associated there with in a reverse direction. The second terminal of the coil 16 is connected through a condenser 17 to the grid circuit of the triode 2, constituting a reverse feed-back system of the type disclosed in the patent to Rice, No. 1,334,118, whereby the triode 2 is prevented from having any tendency to go into sel'foscillation.

In the modification shown in Fig. 2, a connection is made from the anode circuit of the triode 2 through a condenser 18 to a mid- Way of coils 6 and 7 to the grid of the triode 8. Energy from the oscillator 4. is transferred by way of the resonant circuit 5 to coil 7. The two frequencies produce a beat phenomena which is resolved and detected by the triode 8 to a lower radio frequency and then amplified and detected to audio frequency signals by the amplifiers 11 and detector 12.

In the first embodiment of my invention, just described, the triode 2 is prevented from self-oscillation by the presence of the reverse feed-back obtained by the combination of the coil 16 and condenser 17. In the operation of the system, energy from the local oscillator 4 is impressed upon the coil 7 and some energy is unavoidably impressed upon coil 6, because of its coupling thereto and the pro duction of potential differences therein. Energy is also simultaneously impressed upon the coil 16 which, being wound in reverse direction and closely coupled thereto, causes the development of potential in a reverse phase. The capacitance of condenser 17 is made approximately equal to the inter-electrode capacity of the triode 2 and, therefore,

' the energy impressed upon the grid of the triode 2 from the coils 6 and 16 consists of two components, which are substantially equal and opposite in phase and are thereby mutuallyneutralized. In consequence thereof, no local energy is impressed upon, or radiated from, the receptor 1.

Simultaneously, the introduction of the second tuned circuit consisting of the coil 7 and the condenser 15, provides an additional filter trap which increases the selectivity of the system to incoming signals. The filter trap is made resonant to the desired signals and being non-resonant to other frequencies, re ects undesired slgnals. Likewlse, the presence of the two resonant clrcuits and the presence of the triode 2 attenuates the amfrequency is made.

The embodiment of my invention shown in Fig. 2 operates in a substantially similar manner and obtains similar resultsto thefirst described embodiment, with the exception that energy from the local oscillation generator is allowed topass simultaneously to the inter-electrode capacitance of the triode 2 to the grid thereof and simultaneously in reverse phase through half of the loop antenna 1 thereby inducing in the other half thereof currents in reverse phase which are impressed upon the grid of triode 2. The presence of the second described currents impressed from the loop 1 upon the grid of triode 2 neutralizes the currents induced directly through the inter-electrode capacitance and thereby prevents local oscillation of the triode 2 and allows it to respond only to incoming signals.

While I have shown and described but two embodiments of my invention, it is capable of various changes and modifications therefrom without departing from the spirit thereof and it is desired therefore that only such limitations shall be imposed thereon as are indicated in the prior art' or in the appended claims.

I claim as my invention:

1. In a radio receiving system, a receiving circuit capable of radiating, means associated therewith and including a local source of oscillations for heterodyning an incoming signal to a different frequency, a vacuumtube device and a circuit network interposed between said local source and said receiving circuit, and connections between said receiv- -ing circuit, said vacuum tube and said network such that oscillations from "said local through said network and said vacuum tube in opposing phase relation, whereby said 10- cally generated oscillations are prevented source are impressed on the receiving circuit from being radiated by said receiving cir- 1 cuit.

2. In a radio receivin system, a receiving circuit capable of radiating, a local source of oscillations for heterodyning an incoming duce said different frequency, and connections between said receiving circuit, said vacuum tube and said network such that oscillations from said local source may be impressed on the receiving circuit in opposing phase.

In testimony whereof, I have hereunto subscribed my name this 3rd day of February,

GEORGE L. BEERS. 

